diff options
Diffstat (limited to 'src/backend/storage')
| -rw-r--r-- | src/backend/storage/smgr/md.c | 28 | ||||
| -rw-r--r-- | src/backend/storage/smgr/smgr.c | 14 |
2 files changed, 30 insertions, 12 deletions
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c index 825b58dc416..31904741db1 100644 --- a/src/backend/storage/smgr/md.c +++ b/src/backend/storage/smgr/md.c @@ -827,19 +827,21 @@ mdnblocks(SMgrRelation reln, ForkNumber forknum) /* * mdtruncate() -- Truncate relation to specified number of blocks. + * + * Guaranteed not to allocate memory, so it can be used in a critical section. + * Caller must have called smgrnblocks() to obtain curnblk while holding a + * sufficient lock to prevent a change in relation size, and not used any smgr + * functions for this relation or handled interrupts in between. This makes + * sure we have opened all active segments, so that truncate loop will get + * them all! */ void -mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks) +mdtruncate(SMgrRelation reln, ForkNumber forknum, + BlockNumber curnblk, BlockNumber nblocks) { - BlockNumber curnblk; BlockNumber priorblocks; int curopensegs; - /* - * NOTE: mdnblocks makes sure we have opened all active segments, so that - * truncation loop will get them all! - */ - curnblk = mdnblocks(reln, forknum); if (nblocks > curnblk) { /* Bogus request ... but no complaint if InRecovery */ @@ -1108,7 +1110,7 @@ _fdvec_resize(SMgrRelation reln, reln->md_seg_fds[forknum] = MemoryContextAlloc(MdCxt, sizeof(MdfdVec) * nseg); } - else + else if (nseg > reln->md_num_open_segs[forknum]) { /* * It doesn't seem worthwhile complicating the code to amortize @@ -1120,6 +1122,16 @@ _fdvec_resize(SMgrRelation reln, repalloc(reln->md_seg_fds[forknum], sizeof(MdfdVec) * nseg); } + else + { + /* + * We don't reallocate a smaller array, because we want mdtruncate() + * to be able to promise that it won't allocate memory, so that it is + * allowed in a critical section. This means that a bit of space in + * the array is now wasted, until the next time we add a segment and + * reallocate. + */ + } reln->md_num_open_segs[forknum] = nseg; } diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c index 7d667c6586f..fc0516c1eb0 100644 --- a/src/backend/storage/smgr/smgr.c +++ b/src/backend/storage/smgr/smgr.c @@ -59,7 +59,7 @@ typedef struct f_smgr BlockNumber blocknum, BlockNumber nblocks); BlockNumber (*smgr_nblocks) (SMgrRelation reln, ForkNumber forknum); void (*smgr_truncate) (SMgrRelation reln, ForkNumber forknum, - BlockNumber nblocks); + BlockNumber old_blocks, BlockNumber nblocks); void (*smgr_immedsync) (SMgrRelation reln, ForkNumber forknum); } f_smgr; @@ -548,10 +548,15 @@ smgrnblocks(SMgrRelation reln, ForkNumber forknum) * * The caller must hold AccessExclusiveLock on the relation, to ensure that * other backends receive the smgr invalidation event that this function sends - * before they access any forks of the relation again. + * before they access any forks of the relation again. The current size of + * the forks should be provided in old_nblocks. This function should normally + * be called in a critical section, but the current size must be checked + * outside the critical section, and no interrupts or smgr functions relating + * to this relation should be called in between. */ void -smgrtruncate(SMgrRelation reln, ForkNumber *forknum, int nforks, BlockNumber *nblocks) +smgrtruncate(SMgrRelation reln, ForkNumber *forknum, int nforks, + BlockNumber *old_nblocks, BlockNumber *nblocks) { int i; @@ -576,7 +581,8 @@ smgrtruncate(SMgrRelation reln, ForkNumber *forknum, int nforks, BlockNumber *nb /* Do the truncation */ for (i = 0; i < nforks; i++) { - smgrsw[reln->smgr_which].smgr_truncate(reln, forknum[i], nblocks[i]); + smgrsw[reln->smgr_which].smgr_truncate(reln, forknum[i], + old_nblocks[i], nblocks[i]); /* * We might as well update the local smgr_fsm_nblocks and |